diff --git a/twander.py b/twander.py
index 8c27f54..2758d21 100755
--- a/twander.py
+++ b/twander.py
@@ -4,7 +4,7 @@
 # For Updates See:  http://www.tundraware.com/Software/twander
 
 PROGNAME = "twander"
-RCSID = "$Id: twander.py,v 2.18 2002/12/15 23:19:23 tundra Exp $"
+RCSID = "$Id: twander.py,v 2.19 2002/12/17 00:58:23 tundra Exp $"
 VERSION = RCSID.split()[2]
 
 
@@ -510,6 +510,18 @@
     # field.  If it is a 3rd field, it is not
     # a variable definition, but a command definition.
     #
+    # If the LHS is one of the Program Function Names
+    # used in key binding, the statement is understood
+    # to be a key rebinding, not a user variable definition.
+    #
+    # Finally, the LHS cannot be one of the program
+    # builtin variables - it is an error, for example,
+    # to have something like:
+    #
+    #        DIR = string
+    #
+    # because "DIR" is a builtin variable name.
+    #
 
     elif ((dummy[0].count(ASSIGN) + dummy[1].count(ASSIGN)) > 0) and (fields[0][0] != ASSIGN):
         
@@ -517,8 +529,13 @@
         name = line[:assign].strip()
         val=line[assign+1:].strip()
 
-        # Warn on variable redefinitions
-        if UI.SymTable.has_key(name):
+        # Error out on variable redefinitions of either
+        # existing user-defined variables or built-ins
+        
+        if UI.SymTable.has_key(name) or \
+           UI.BuiltIns.has_key('[' + name + ']') or \
+           UI.BuiltIns.has_key('[' + name):
+            
             ErrMsg(eREDEFVAR % (name, num, line))
             sys.exit(1)